The present invention relates to a product, a process for its preparation and the use of such in plastic film production. More specifically, the present invention relates to an antiblock talc, a process for the preparation of such and its use as an additive in the production of polyolefin film.
Polyolefin films produced according to the process of the present invention are useful in a broad range of packaging and film covering applications.
Polyolefin films are used extensively for packaging and in film covering applications. The use of polyolefin films continues to increase as new market opportunities become available in areas where paper was traditionally used. The versatility of the film provides potentially infinite growth prospects for the product in the future. However, there is an inherent short coming in the use of plastic films that may retard its market acceptance and growth, it sticks. When plastic film is produced or used in various applications, there is a tendency for contacting layers of the film to stick together or xe2x80x9cblockxe2x80x9d, making separation of the film, opening of bags made from the film, or finding the end of the film on plastic rolls difficult. The present invention relates to polyolefin resin compositions that are specifically designed to have satisfactory antiblocking capability.
Antiblock agents are materials that are added to polyolefin resins to roughen their surface and thereby prevent layers of the plastic film from sticking, hence the term, xe2x80x9cantiblocking agentxe2x80x9d is applied to such materials. Although, inorganic minerals, such as, for example, diatomaceous earth, synthetic silica and talc are known to reduce blocking when added to polyolefin film resin compositions, each has both advantages and critical disadvantages.
One comparative advantage of diatomaceous earth is that it is known to be a moderately effective antiblocking agent, when used as an antiblocking agent. However, it is also known that diatomaceous earth adversely affects the film""s physical properties, such as film clarity, film haze, and is very abrasive and moderately expensive and may pose a serious health threat. Synthetic silicates are known to be effective as an antiblock, however a significant disadvantage of silica is that it is very expensive. Talc, on the other hand, has found increasing use as an effective antiblock agent over diatomaceous earth and synthetic silica because of a significant cost advantage over both. However, one major disadvantage when talc is added to polyolefin film resins, is that it aggressively adsorbs other film additives, such as antioxidants, slip agents and processing aid. The absence, or reduced level of these additives in polyolefin resin compositions during production, routinely cause processing problems and raise serious film quality concerns.
For example, antioxidants are added to improve film stability, slip agents are present in the resin to improve film converting, while processing aids are employed to improve film quality, and to provide lubrication during film extrusion by eliminating melt fracture. Melt fracture is a measure of film surface uniformity, appearance and strength. Of the three additives mentioned here, processing aids are most adversely affected by the presence of antiblock agents. Although it is well known that all antiblock agents adsorb processing aids, talc antiblock agents adsorb greater levels of processing aids than either diatomaceous earth or synthetic silica antiblocks. Consequently, when resin compositions are produced having additives that include antiblock talc, it is necessary to increase the dosage of processing aids. The increased dosage adversely effects the over all production economics of the plastic film.
Therefore, what is needed is a new generation of talc antiblock agents that adsorb less process aids than either synthetic silica or diatomaceous earth.
U.S. Pat. No. 5,401,482, discloses a method for the manufacture of a talc substance consisting of particles having a sheet structure, each particle having an internal crystalline structure and at least one hydrophilic surface, the method comprising heating talc particles to a temperature below 900 degrees Centigrade under conditions such as to avoid conversion of the talc into enstatite and in order to effect a surface modification consisting of substituting inert siloxane groups by active silanols.
U.S. Pat. No. 5,229,094 discloses a talc substance consisting of particles having a sheet structure, each particle comprising internal hydrophobic sheets, having the crystalline structure of talc within each unit and bonded together by cohesion forces typical of talc (Van der Waals forces), the talc substance being characterized in that each particle has at least one hydrophilic surface sheet.
A product and a method for producing an antiblock agent comprising surface treating an inorganic mineral with a functionalized siloxane polymer or a polyether polymer or functionalized polyether polymer or carbon based polymer. When inorganic minerals are coated with a functionalized siloxane polymer or a polyether polymer or a functionalized polyether polymer or carbon based polymer and subsequently used as an additive in the production of polyolefin film, the adsorption of other resin additives is substantially reduced.
Polyolefin films produced according to the process of the present invention are useful in a broad range of packaging and film covering applications.
In one aspect the present invention embodies surface treating talc with certain types of silanes or siloxane polymers. The treated talc inhibits the adsorption of plastic film additives onto the talc. Surface treating means coating, partially coating, or using an effective amount to inhibit the adsorption of other additives. The invention embodies of coating any talc material with a functionalized polydialkyl, preferably polydimethylsiloxane, having the structural formula:
[Si(CH3)(R)xe2x80x94Oxe2x80x94Si(CH3)(R)xe2x80x94O]n
where n is the number of repeating units (molecular weight), CH3 is a methyl group, Si is silicon, O is oxygen, and R is a functionalized alkyl group. The alkyl group may, without limitation, be functionalized with carboxylate, amine, amide, thiol, sulfate, phosphate, and the like.
Siloxane polymers that are useful in the present invention may be selected from the group consisting of finctionalized alkyl polydimethylsiloxane (carboxylate, amine, amide, thiol, sulfate, phosphate) wherein carboxylate is preferred, Bis-(12-hydroxystearate) terminated polydimethylsiloxane (Aldrich Chemical Co.xe2x80x941001 West Saint Paul Avenue, Milwaukee, Wis. 53233), and Poly(Dimethylsiloxane)-Graft-Polyacrylates (Aldrich). There is no limitation on the method used to produce the siloxane polymers. The siloxane polymers of the present invention may be manufactured by ionic polymerization or radical polymerization and the like, or any other process known to produce siloxane polymers.
The molecular weight range of the siloxane polymer is from about 1000 to about 1,000,000 atomic mass units (a.m.u.), preferably ranges from about 1000 to about 100,000 a.m.u. The molecular weight can be determined by gel permeation chromatography (GPC).
Silanes that are useful in the present invention have the structural formula SiR4, where Si is silicon, R can be any group capable of forming a covalent bond with silicon (e.g., an alkyl group, an alkoxy group, a functionalized alkyl group, and a functionalized alkoxy group, and any combination thereof). The following silanes are useful in the present invention: Octyltriethoxysilane (OSi Silquest(copyright) A-137 silane), Triamino functional silane (OSi Silquest(copyright) A-1130 silane), Bis-(gamma-trmethoxysilylpropyl) amine (OSi Silquest(copyright) A-1170 silane), all of which are commercially available from OSi.
In another aspect, the present invention consists of coating talc with polyethers and functionalized polyethers to reduce film additive adsorption onto the talc. The general structural formula is:
Hxe2x80x94(OCHR(CH2)xCHRl)nxe2x80x94OH
where n is the number of repeating units (molecular weight), x is zero or an integer, R is an alkyl group, O is oxygen, C is carbon, H is hydrogen, and R1 is a functional group which may be, without limitation, an alkyl carboxylate, an alkyl amine, an alkyl amide, analkyl thiol, an alkyl sulfate, an alkyl sulfonate, an alkyl phosphate or an alkyl phosphonate and the like.
Polyethers and functionalized polyethers that are useful for the surface treatment of talc may be selected from the group consisting of poly(ethylene glycol), poly (ethylene glycol) Bis-(carboxymethyl) ether, poly (ethylene glycol) dimethyl ether, poly (ethylene glycol-400) distearate, and the like, and functionalized polyethers (alkyl carboxylate, alkyl amine, alkyl amride, alkyl sulfate, alkyl thiol, alkyl sulfonate, alkyl phosphate, alkyl phosphonate) wherein alkyl carboxylate functionality is preferred. There is no limitation on the method used to produce the polyethers and functionalized polyether polymers. The polyethers and functionalized polyethers of the present invention may be manufactured by ionic polymerization or radical polymerization and the like, or by any other process known to produce polyethers and functionalized polyethers.
The molecular weight range of the polyethers and functionalized polyethers is from about 1000 to about 10,000,000 a.m.u., with a preferred range of from about 10,000 to about 1,000,000 a.m.u. The molecular weight can be determined by GPC.
In a further aspect the present invention pertains to the use of carbon based polymer coatings for surface treating the talc in order to lower the level of additive adsorption. Also included in the definition of carbon based polymers are maleic acid/olefin co-polymers having the general formula: 
where n denotes molecular weight and x and y represent the ratio of each monomeric unit in the polymer. Carbon based polymers that are useful for the surface treatment of talc may be selected from the group consisting of functionalized polyolefins: maleic acid/olefin copolymer, maleic acid/styrene copolymer, wherein maleic acid/styrene copolymer is preferred. Also included in the carbon-based polymers group are mineral oils of any boiling point and paraffin waxes of any melting point. The x/y ratio can range from about 100:1 to about 1:100, wherein the preferred range is from about 10:1 to about 1:10. C is carbon, O is oxygen, H is hydrogen and R is a functional group. R may be any group that can form a bond with carbon. This includes, without limitation, alkyl carboxylates, alkyl amines, alkyl amides, alkyl thiols, alkyl sulfates, alkyl sulfonates, alkyl phosphates, and alkyl phosphonates and the like.
The molecular weight of the carbon based polymer may range from about 100 to about 10,000,000 a.m.u., with a preferred range of from about 200 to about 2,000,000 a.m.u.
Any inorganic mineral, such as, talc, calcium carbonate, precipitated calcium carbonate, clay or silica, that is receptive to surface treatment may be coated with the polymers described herein. However, talc is the preferred inorganic mineral. Talcs that are particularly useful are those that are receptive to both surface treatment and that are capable of subsequent use in polyolefin film production. An exemplary, but nonlimiting talc, would typically have an empirical formula of Mg3Si4O10(OH)2, and a specific gravity of from about 2.6 to about 2.8. The preferred talc, without other limitations, could have an average particle size of from about 0.1 microns to about 10 microns, wherein the preferred average particle size is from about 0.5 microns to about 5 microns. The talc may be coated with from about 0.01 weight percent to about 10 percent of the polymers described herein, wherein the preferred treatment level for coating is from about 0.25 weight percent to 2 weight percent, based on the weight of the polymer.
All of the polymer coatings described herein may be applied to talc by any convenient dry powder mixing operation. The temperature at which the coating is applied to the talc, ranges from about 0 zero degrees Centigrade (C) to about 500 degrees C., preferably from about 30 degrees C. to about 200 degrees C., and more preferably, from about 60 degrees C. to about 80 degrees C. The application temperature should be adjusted to higher levels if the specific coating requires melting. Once the talc is coated, an antiblock talc is produced that may be used, by those skilled in the art, just as any other commercially available antiblock. For example, but without limitations, the coated antiblock talc may be added to the film extruder or added as an already compounded masterbatch to the extruder. A compounded masterbatch means the resin and the antiblock are pre-mixed in a compounder before being added to the film extruder.
Polyolefins considered suitable for the present invention may be any polyolefin, which can be clear, crystalline, and capable of forming a self-supported film. Non-limiting examples include crystalline homopolymers of xcex1-olefin with carbon numbers ranging from 2 to 12 or a blend of two or more crystalline copolymers or ethylene-vinylacetate copolymers with other resins. Also, the polyolefin resin can be a high-density polyethylene, low density polyethylene, linear low-density polyethylene, polypropylene, ethylene-propylene copolymers, poly-1-butene, ethylene-vinyl acetate copolymers, etc., and low and medium-density polyethylenes. Additional examples are represented by random or block copolymers of polyethylene, polypropylene poly-r-methylpentene-1, and ethylene-propylene, and ethylene-propylene-hexane copolymers. Among them, copolymers of ethylene and propylene and those containing 1 or 2 selected from butene-1, hexane-1, 4-methylpentene-1, and octene-1 (the so-called LLDPE) are particularly suitable.
The method of producing polyolefin resin used in the present invention is not limited. For example, it can be manufactured by ionic polymerization or radical polymerization. Examples of polyolefin resins obtained by ionic polymerization include homopolymers such as polyethylene, polypropylene, polybutene-2, and poly-4-methylpentene and ethylene copolymers obtained by copolymerizing ethylene and xcex1-olefin, xcex1-olefins having from 3 to 18 carbon atoms such as propylene, butene-1,4-methylpentene-1, hexene-1, octene-1, decene-1, and octadecene-1 are used as xcex1-olefins. These xcex1-olefins can be used individually or as two or more types. Other examples include propylene copolymers such as copolymers of propylene and butene-1. Examples of polyolefin resins obtained by radical polymerization include ethylene alone or ethylene copolymers obtained by copolymerizing ethylene and radical polymerizable monomers. Examples of radical polymerizable monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid and maleic acid esters and acid anhydrides thereof, and vinyl esters such as vinyl acetate. Concrete examples of esters of unsaturated carboxylic acids include ethyl acrylate, methyl methacrylate and glycidyl methacrylate. These radical polymerizable monomers can be used individually or as two or more types.
A typical embodiment of the present invention could include:
A typical preferred embodiment of the present invention includes:
All percentages are based on total weight percent.
1. Extruders. The following extruders were used to measure the effect of antiblocks on process aid (PA) performance.
a. Brabender Single Screw Tape Die Extruder
b. ZSK co-rotating low intensity twin screw extruder
c. Lestritz low intensity counter-rotating twin screw extruder
d. Welex Extruder
2. Henshal Mixer. Used for mixing the siloxane, or silane, or polyether, or carbon based polymer and antiblock compounds.
3. Killion Blown Film Line. This is a 1xc2xc inch extruder with a L/D ratio of 30:1 and 2xc2xd inch die with a 12 mm die gap. The temperature profile of the extruder and the blown film line were 177xc2x0 C., 93xc2x0 C., 193xc2x0 C., 204xc2x0 C., 204xc2x0 C., 204xc2x0 C., 204xc2x0 C., 204xc2x0 C., 204xc2x0 C., and 204xc2x0 C. with a melt temperature of 200-208xc2x0 C. Output was about 9 lbs/hr. with a sheer rate of 500 secxe2x88x921. Die pressure and melt fracture reduction were monitored every 15 minutes for two hours.
Extrusionxe2x80x94fundamental processing operation in which a material is forced through a metal forming die, followed by cooling or chemical hardening (see Hawley""s Condensed Chemical Dictionary, 12th Edition 1993, page 505).
Diexe2x80x94a device having a specific shape or design in which it imparts to plastic by passing the material through it (estrusion). Die extruders are used to measure the effect of anti-blocks on process aid (PA) performance.
Tape Die Extrusionxe2x80x94extrusion procedure for measuring process aid demand based on the amount of process aid required to reduce die pressure and eliminate melt fracture.
Antiblockxe2x80x94materials that roughen the surface of plastic films to reduce their tendency to stick together. These materials may include synthetic silica, diatomaceous earth (DE), and talc.
Clarity Antiblockxe2x80x94a type of antiblock that is added when compounding chemicals, to reduce opacity and to improve the clarity of the polymer film.
Process Aid (PA)xe2x80x94provides lubrication or slip at the die during film extrusion which improves film quality by elimination of melt fracture. Process aids are evaluated on pressure reduction (less PA absorbed) and elimination of melt fracture (percent melt fracture).
Die Pressurexe2x80x94Pressure at the die. Die pressure reduction is how well the process aid is performing, meaning that the process aid is not absorbed by the talc and hence, is available to reduce die pressure.
Melt Fracturexe2x80x94a measure of film surface uniformity. The objective is complete elimination of melt fracture. Melt fracture is monitored as a function of time at a given PA dosage and measured in a rate conditioning test.
Rate of Conditioningxe2x80x94Technique used by film manufacturers to determine process aid (PA) performance and to determine the effect of a given antiblock on PA effectiveness. This is done using tape die extrusion and monitoring die pressure and percent melt fracture over a period of time.
ABT-Gxe2x80x94an ABT 2500(copyright) talc coated with an amine functionalized siloxane (Genese Polymers, GP-4).
Functional Groupsxe2x80x94The arrangements of atoms and groups of atoms that occur repeatedly in an organic substance.
Blown Film Testxe2x80x94Type of extrusion that after the polymer compounded is formed to its desired thickness by air being blown through a cylindrical die.
Antioxidantxe2x80x94An organic compound added to plastics to retard oxidation, deterioration, rancidity, and gum formation (see Hawley""s Condensed Chemical Dictionary, 12th Edition 1993, page 90).
Feldsparxe2x80x94General name for a group of sodium, potassium, calcium, and barium aluminum silicates (see Hawley""s Condensed Chemical Dictionary, 12th Edition 1993, page 509).
Diatomaceous earth (DE)xe2x80x94Soft, bulky, solid material (88% silica) composed of small prehistoric aquatic plants related to algea (diatoms). Absorbs 1.5 to 4 times its weight of water, also has high oil absorption capacity (see Hawley""s Condensed Chemical Dictionary, 12th Edition 1993, page 365).
Paraffin (alkane)xe2x80x94a class of aliphatic hyrdocarbons characterized by a straight or branched carbon chain (CnH2n+2) (see Hawley""s Condensed Chemical Dictionary, 12th Edition 1993, page 871).